This invention relates to combustion control directed to maintaining fuel efficiency and minimal emissions of air pollutants, especially nitrogen oxides (NOx). More particularly, the invention provides a combustion control system to maintain a selected fuel-air ratio that is improved in that density changes of a reactant, usually air, caused by temperature variations, are compensated for.
Two types of combustion control systems are commonly used (both illustrated in FIGS. 1 and 2 hereof). One is known as the “jack-shaft” or “single-point” positioning system, and the other as a “two-point parallel” system. U.S. Pat. No. 4,249,886 to Bush discusses both types of combustion control systems and proposes modification of the linkage that controls fuel and air flow. The modified linkage is intended to change the air flow in relation to any desired changes in fuel flow. However, the Bush control system fails to compensate for temperature changes in the reactants, principally significant temperature swings of air which obviously change air density and thus cause the fuel-air ratio to vary from the desired or target ratio.
A principal object of this invention is to provide an improved combustion control system that in response to temperature changes of the reactants, usually air alone, automatically varies the flow of fuel or air to maintain a substantially constant target fuel-air ratio.
Another object is to minimize the use of mechanical linkages in the control system.
These and other features and advantages of the invention will be apparent from the description which follows.